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<meta name="description" content="关键词：函数，大小端转换，数码管译码 在 Verilog 中，可以利用任务（关键字为 task）或函数（关键字为 function），将重复性的行为级设计进行提取，并在多个地方调用，来避免重复代码的多次编写，使代码更加的简洁、易懂。 函数 函数只能在模块中定义，位置任意，并在模块的任何地方引用，作用范围也局限于此模块。函数主要有以下几个特点：  1）不含有任何延迟、时序或时序控制逻辑 2）至少有一个输入变量 3）只有一个返回值，且没有输..">
		
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				<h2>6.1 Verilog 函数</h2>				<h3><em>分类</em> <a href="../w3cnote_genre/verilog" title="Verilog 教程" >Verilog 教程</a> </h3>
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					<h3>关键词：函数，大小端转换，数码管译码</h3>
<p>在 Verilog 中，可以利用任务（关键字为 task）或函数（关键字为 function），将重复性的行为级设计进行提取，并在多个地方调用，来避免重复代码的多次编写，使代码更加的简洁、易懂。
</p><h3>函数</h3><p>
函数只能在模块中定义，位置任意，并在模块的任何地方引用，作用范围也局限于此模块。函数主要有以下几个特点：</p>
<ul><li>
1）不含有任何延迟、时序或时序控制逻辑</li><li>
2）至少有一个输入变量</li><li>
3）只有一个返回值，且没有输出</li><li>
4）不含有非阻塞赋值语句</li><li>
5）函数可以调用其他函数，但是不能调用任务</li></ul>
<p>Verilog 函数声明格式如下：</p>
<pre>function [range-1:0]     function_id ;
input_declaration ;
 other_declaration ;
procedural_statement ;
endfunction</pre>
 <p>
函数在声明时，会隐式的声明一个宽度为 range、 名字为 function_id 的寄存器变量，函数的返回值通过这个变量进行传递。当该寄存器变量没有指定位宽时，默认位宽为 1。</p><p> 
函数通过指明函数名与输入变量进行调用。函数结束时，返回值被传递到调用处。</p><p>
函数调用格式如下：</p>
<pre>function_id(input1, input2, &hellip;);</pre>
 <p>
下面用函数实现一个数据大小端转换的功能。</p><p>
当输入为 4'b0011 时，输出可为 4'b1100。例如：</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #A52A2A; font-weight: bold;">module</span> endian_rvs<br />
&nbsp; &nbsp; <span style="color: #5D478B;">#</span><span style="color: #9F79EE;">&#40;</span><span style="color: #A52A2A; font-weight: bold;">parameter</span> N <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">4</span><span style="color: #9F79EE;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #9F79EE;">&#40;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; en<span style="color: #5D478B;">,</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//enable control</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; a <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">output</span> <span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp;b<br />
&nbsp; &nbsp; <span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">reg</span> <span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;b_temp <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">always</span> <span style="color: #5D478B;">@</span><span style="color: #9F79EE;">&#40;</span><span style="color: #5D478B;">*</span><span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">if</span> <span style="color: #9F79EE;">&#40;</span>en<span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; b_temp <span style="color: #5D478B;">=</span> &nbsp;data_rvs<span style="color: #9F79EE;">&#40;</span>a<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">else</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; b_temp <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">0</span> <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">assign</span> b <span style="color: #5D478B;">=</span> b_temp <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<br />
&nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//function entity</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">function</span> <span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; data_rvs <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> &nbsp; &nbsp; <span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> data_in <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">parameter</span> &nbsp; &nbsp; &nbsp; &nbsp; MASK <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">3</span><span style="color: #ff0055;">2'h3</span> <span style="color: #5D478B;">;</span> <br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; k <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">for</span><span style="color: #9F79EE;">&#40;</span>k<span style="color: #5D478B;">=</span><span style="color: #ff0055;">0</span><span style="color: #5D478B;">;</span> k<span style="color: #5D478B;">&lt;</span>N<span style="color: #5D478B;">;</span> k<span style="color: #5D478B;">=</span>k<span style="color: #5D478B;">+</span><span style="color: #ff0055;">1</span><span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; data_rvs<span style="color: #9F79EE;">&#91;</span>N<span style="color: #5D478B;">-</span>k<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #9F79EE;">&#93;</span> &nbsp;<span style="color: #5D478B;">=</span> data_in<span style="color: #9F79EE;">&#91;</span>k<span style="color: #9F79EE;">&#93;</span> <span style="color: #5D478B;">;</span> &nbsp;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">endfunction</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<br />
<span style="color: #A52A2A; font-weight: bold;">endmodule</span> &nbsp; &nbsp; &nbsp; &nbsp;<br />
</div></div><p>
函数里的参数也可以改写，例如：</p><pre>
defparam data_rvs.MASK = 32'd7 ;</pre><p>
但是仿真时发现，此种写法编译可以通过，仿真结果中，函数里的参数 MASK 实际并没有改写成功，仍然为 32'h3。这可能和编译器有关，有兴趣的学者可以用其他 Verilog 编译器进行下实验。</p><p>
函数在声明时，也可以在函数名后面加一个括号，将 input 声明包起来。</p>
<p>例如上述大小端声明函数可以表示为：</p>
<pre>function [N-1:0]     data_rvs（
input     [N-1:0] data_in 
    ......
&nbsp;&nbsp;&nbsp;&nbsp;） ;</pre>

<h3>常数函数</h3><p>
常数函数是指在仿真开始之前，在编译期间就计算出结果为常数的函数。常数函数不允许访问全局变量或者调用系统函数，但是可以调用另一个常数函数。</p>
<p>这种函数能够用来引用复杂的值，因此可用来代替常量。</p>
<p>例如下面一个常量函数，可以来计算模块中地址总线的宽度：</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #A52A2A; font-weight: bold;">parameter</span> &nbsp; &nbsp;MEM_DEPTH <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">256</span> <span style="color: #5D478B;">;</span><br />
<span style="color: #A52A2A; font-weight: bold;">reg</span> &nbsp;<span style="color: #9F79EE;">&#91;</span>logb2<span style="color: #9F79EE;">&#40;</span>MEM_DEPTH<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span> <span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> addr <span style="color: #5D478B;">;</span> <span style="color: #00008B; font-style: italic;">//可得addr的宽度为8bit</span><br />
&nbsp;<br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">function</span> <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; logb2<span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; depth <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//256为9bit，我们最终数据应该是8，所以需depth=2时提前停止循环</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">for</span><span style="color: #9F79EE;">&#40;</span>logb2<span style="color: #5D478B;">=</span><span style="color: #ff0055;">0</span><span style="color: #5D478B;">;</span> depth<span style="color: #5D478B;">&gt;</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">;</span> logb2<span style="color: #5D478B;">=</span>logb2<span style="color: #5D478B;">+</span><span style="color: #ff0055;">1</span><span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span> <br />
&nbsp; &nbsp; &nbsp; &nbsp; depth <span style="color: #5D478B;">=</span> depth <span style="color: #5D478B;">&gt;&gt;</span> <span style="color: #ff0055;">1</span> <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
<span style="color: #A52A2A; font-weight: bold;">endfunction</span><br />
</div></div>

<h3>automatic 函数</h3>
<p>在 Verilog 中，一般函数的局部变量是静态的，即函数的每次调用，函数的局部变量都会使用同一个存储空间。若某个函数在两个不同的地方同时并发的调用，那么两个函数调用行为同时对同一块地址进行操作，会导致不确定的函数结果。</p>
<p>Verilog 用关键字 automatic 来对函数进行说明，此类函数在调用时是可以自动分配新的内存空间的，也可以理解为是可递归的。因此，automatic 函数中声明的局部变量不能通过层次命名进行访问，但是 automatic 函数本身可以通过层次名进行调用。</p>
<p>下面用 automatic 函数，实现阶乘计算：</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #A52A2A; font-weight: bold;">wire</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">31</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;results3 <span style="color: #5D478B;">=</span> factorial<span style="color: #9F79EE;">&#40;</span><span style="color: #ff0055;">4</span><span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
<span style="color: #A52A2A; font-weight: bold;">function</span> <span style="color: #A52A2A; font-weight: bold;">automatic</span> &nbsp; <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; &nbsp; &nbsp; factorial <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; data <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">integer</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; i <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; factorial <span style="color: #5D478B;">=</span> <span style="color: #9F79EE;">&#40;</span>data<span style="color: #5D478B;">&gt;=</span><span style="color: #ff0055;">2</span><span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">?</span> data <span style="color: #5D478B;">*</span> factorial<span style="color: #9F79EE;">&#40;</span>data<span style="color: #5D478B;">-</span><span style="color: #ff0055;">1</span><span style="color: #9F79EE;">&#41;</span> <span style="color: #5D478B;">:</span> <span style="color: #ff0055;">1</span> <span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
<span style="color: #A52A2A; font-weight: bold;">endfunction</span> <span style="color: #00008B; font-style: italic;">// factorial</span><br />
</div></div>
<p>
下面是加关键字 automatic 和不加关键字 automatic 的仿真结果。</p><p>
由图可知，信号 results3 得到了我们想要的结果，即 4 的阶乘。</p><p>
而信号 results_noauto 值为 1，不是可预知的正常结果，这里不再做无用分析。</p>
<p><img decoding="async" src="https://www.runoob.com/wp-content/uploads/2020/09/7D8rIxoto57d5oIH.png"></p>

<h3>数码管译码</h3><p>
上述中涉及的相关函数知识似乎并没有体现出函数的优越性。下面设计一个 4  位 10 进制的数码管译码器，来说明函数可以简化代码的优点。</p>
<p>下图是一个数码管的实物图，可以用来显示 4 位十进制的数字。在比赛计分、时间计时等方面有着相当广泛的应用。</p>
<p><img decoding="async" src="https://www.runoob.com/wp-content/uploads/2020/09/Opby8zp1J4qnFKBC.jpg"  /></p>
<p>
每位数码显示端有 8 个光亮控制端（如图中 a-g 所示），可以用来控制显示数字 0-9 。</p><p>
而数码管有 4 个片选（如图中 1-4），用来控制此时哪一位数码显示端应该选通，即应该发光。倘若在很短的时间内，依次对 4 个数码显示端进行片选发光，同时在不同片选下给予不同的光亮控制（各对应 4 位十进制数字），那么在肉眼不能分辨的情况下，就达到了同时显示 4 位十进制数字的效果。</p><p>
<img decoding="async" src="https://www.runoob.com/wp-content/uploads/2020/09/0gKIiA8KbAttgnU3.jpg"></p>
<p>下面，我们用信号 abcdefg 来控制光亮控制端，用信号 csn 来控制片选，4 位 10 进制的数字个十百千位分别用 4 个 4bit 信号 single_digit, ten_digit, hundred_digit, kilo_digit 来表示，则一个数码管的显示设计可以描述如下：</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: #A52A2A; font-weight: bold;">module</span> digital_tube<br />
&nbsp; &nbsp; &nbsp;<span style="color: #9F79EE;">&#40;</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; clk <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; rstn <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; en <span style="color: #5D478B;">,</span><br />
&nbsp;<br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; single_digit <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; ten_digit <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; hundred_digit <span style="color: #5D478B;">,</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; kilo_digit <span style="color: #5D478B;">,</span><br />
&nbsp;<br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">output</span> <span style="color: #A52A2A; font-weight: bold;">reg</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp;csn <span style="color: #5D478B;">,</span> <span style="color: #00008B; font-style: italic;">//chip select, low-available</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">output</span> <span style="color: #A52A2A; font-weight: bold;">reg</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">6</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp;abcdefg &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #00008B; font-style: italic;">//light control</span><br />
&nbsp; &nbsp; &nbsp; <span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp;<br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">reg</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">1</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;scan_r <span style="color: #5D478B;">;</span> &nbsp;<span style="color: #00008B; font-style: italic;">//scan_ctrl</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">always</span> <span style="color: #5D478B;">@</span> <span style="color: #9F79EE;">&#40;</span><span style="color: #A52A2A; font-weight: bold;">posedge</span> clk <span style="color: #A52A2A; font-weight: bold;">or</span> <span style="color: #A52A2A; font-weight: bold;">negedge</span> rstn<span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">if</span><span style="color: #9F79EE;">&#40;</span><span style="color: #5D478B;">!</span>rstn<span style="color: #9F79EE;">&#41;</span><span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; csn &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">4'b1111</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abcdefg &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> 'd0<span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; scan_r &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">3'd0</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">else</span> <span style="color: #A52A2A; font-weight: bold;">if</span> <span style="color: #9F79EE;">&#40;</span>en<span style="color: #9F79EE;">&#41;</span> <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">case</span><span style="color: #9F79EE;">&#40;</span>scan_r<span style="color: #9F79EE;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">2'd0</span><span style="color: #5D478B;">:</span><span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; scan_r &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">3'd1</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; csn &nbsp; &nbsp; &nbsp; <span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">4'b0111</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//select single digit</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abcdefg &nbsp; <span style="color: #5D478B;">&lt;=</span> dt_translate<span style="color: #9F79EE;">&#40;</span>single_digit<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">2'd1</span><span style="color: #5D478B;">:</span><span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; scan_r &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">3'd2</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; csn &nbsp; &nbsp; &nbsp; <span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">4'b1011</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//select ten digit</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abcdefg &nbsp; <span style="color: #5D478B;">&lt;=</span> dt_translate<span style="color: #9F79EE;">&#40;</span>ten_digit<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">2'd2</span><span style="color: #5D478B;">:</span><span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; scan_r &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">3'd3</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; csn &nbsp; &nbsp; &nbsp; <span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">4'b1101</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//select hundred digit</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abcdefg &nbsp; <span style="color: #5D478B;">&lt;=</span> dt_translate<span style="color: #9F79EE;">&#40;</span>hundred_digit<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">2'd3</span><span style="color: #5D478B;">:</span><span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; scan_r &nbsp; &nbsp;<span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">3'd0</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; csn &nbsp; &nbsp; &nbsp; <span style="color: #5D478B;">&lt;=</span> <span style="color: #ff0055;">4'b1110</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//select kilo digit</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abcdefg &nbsp; <span style="color: #5D478B;">&lt;=</span> dt_translate<span style="color: #9F79EE;">&#40;</span>kilo_digit<span style="color: #9F79EE;">&#41;</span><span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">endcase</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp;<br />
&nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">/*------------ translate function -------*/</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">function</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">6</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> dt_translate<span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">input</span> <span style="color: #9F79EE;">&#91;</span><span style="color: #ff0055;">3</span><span style="color: #5D478B;">:</span><span style="color: #ff0055;">0</span><span style="color: #9F79EE;">&#93;</span> &nbsp; data<span style="color: #5D478B;">;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">begin</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">case</span><span style="color: #9F79EE;">&#40;</span>data<span style="color: #9F79EE;">&#41;</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd0</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1111110</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 0 -&gt; 0x7e</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd1</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b0110000</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 1 -&gt; 0x30</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd2</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1101101</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 2 -&gt; 0x6d</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd3</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1111001</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 3 -&gt; 0x79</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd4</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b0110011</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 4 -&gt; 0x33</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd5</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1011011</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 5 -&gt; 0x5b</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd6</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1011111</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 6 -&gt; 0x5f</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd7</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1110000</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 7 -&gt; 0x70</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd8</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1111111</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 8 -&gt; 0x7f</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #ff0055;">4'd9</span><span style="color: #5D478B;">:</span> dt_translate <span style="color: #5D478B;">=</span> <span style="color: #ff0055;">7'b1111011</span><span style="color: #5D478B;">;</span> &nbsp; &nbsp; <span style="color: #00008B; font-style: italic;">//number 9 -&gt; 0x7b</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">endcase</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">end</span><br />
&nbsp; &nbsp; <span style="color: #A52A2A; font-weight: bold;">endfunction</span><br />
&nbsp;<br />
<span style="color: #A52A2A; font-weight: bold;">endmodule</span><br />
</div></div>
<p>仿真结果如下。</p><p>
由图可知，片选、译码等信号，均符合设计。实际中，4 位数字应当在一定的时间内保持不变，而片选信号不停的循环扫描，数码管才能给肉眼呈现一种静态显示的效果。</p>
<p><img decoding="async" src="https://www.runoob.com/wp-content/uploads/2020/09/CYfupVhbGAdMtnfn.png" ></p>
 
<h3>小结</h3><p>
如果译码器设计没有使用函数 dt_translate，则在每个 case 选项里对信号 abcdefg 进行赋值时，还需要对 single_digit，ten_digit, hundred_digit, kilo_digit 进行判断。这些判断语句又会重复 4 次。虽然最后综合出的实际硬件电路可能是一样的，但显然使用函数后的代码更加的简洁、易读。</p>
<h3>源码下载</h3>
<p><a href="../wp-content/uploads/2020/09/6.1function.zip" download class="download">Download</a></p>				</div>
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	<a href="javascript:void(0);">Verilog 教程</a>	</div>
	
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		<li>
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	<li><a target="_top" data-id="22999" title="6.4 Verilog 竞争与冒险" href="../w3cnote/verilog-competition-hazard.html" >6.4 Verilog 竞争与冒险</a></li>
	
		
	<li><a target="_top" data-id="23008" title="6.5 Verilog 避免 Latch" href="../w3cnote/verilog-latch.html" >6.5 Verilog 避免 Latch</a></li>
	
		
	<li><a target="_top" data-id="23011" title="6.6 Verilog 仿真激励" href="../w3cnote/verilog-testbench.html" >6.6 Verilog 仿真激励</a></li>
	
		
	<li><a target="_top" data-id="23015" title="6.7 Verilog 流水线" href="../w3cnote/verilog-pipeline-design.html" >6.7 Verilog 流水线</a></li>
	
		
	<li><a target="_top" data-id="23021" title="7.1 Verilog 除法器设计" href="../w3cnote/verilog-dividend.html" >7.1 Verilog 除法器设计</a></li>
	
		
	<li><a target="_top" data-id="23222" title="7.2 Verilog 并行 FIR 滤波器设计" href="../w3cnote/verilog-fir.html" >7.2 Verilog 并行 FIR 滤波器设计</a></li>
	
		
	<li><a target="_top" data-id="23230" title="7.3 Verilog 串行 FIR 滤波器设计" href="../w3cnote/verilog-serial-fir.html" >7.3 Verilog 串行 FIR 滤波器设计</a></li>
	
		
	<li><a target="_top" data-id="23236" title="7.4 Verilog CIC 滤波器设计" href="../w3cnote/verilog-cic.html" >7.4 Verilog CIC 滤波器设计</a></li>
	
		
	<li><a target="_top" data-id="23260" title="7.5 Verilog FFT 设计" href="../w3cnote/verilog-fft.html" >7.5 Verilog FFT 设计</a></li>
	
		
	<li><a target="_top" data-id="23309" title="7.6 Verilog DDS 设计" href="../w3cnote/verilog-dds.html" >7.6 Verilog DDS 设计</a></li>
	
		
	<li><a target="_top" data-id="23281" title="8.1 Verilog 数值转换" href="../w3cnote/verilog-numerical-conversion.html" >8.1 Verilog 数值转换</a></li>
	
	<li><a target="_top" title="Verilog 教程高级篇" href="../w3cnote/verilog2-tutorial.html" >Verilog 教程高级篇</a></li></ul></div>	</div>
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